1. Field of the Invention
The present invention relates to an engine control device having a variable valve mechanism.
2. Description of the Related Art
There has been developed an engine having a variable valve mechanism in a valve system for changing performance characteristics based on the operation state of the engine. The variable valve mechanism is provided between a camshaft and a driven sprocket, and the rotation phase of the camshaft with respect to the driven sprocket can be changed using this variable valve mechanism. More specifically, valve timing can be changed using the variable valve mechanism, and this can control the amount of overlap in which both of an intake valve and an exhaust valve are open. For example, in a low-load operation region of an engine, the valve timing is controlled to reduce the amount of overlap. On the other hand, in a high-load operation region of the engine, the valve timing is controlled to increase the amount of overlap. Accordingly, in various kinds of operation states of the engine, the volume efficiency of the intake air can be improved, and the engine torque can be improved (see Japanese Unexamined Patent Application Publication (JP-A) No. 10-141098).